Pictures shadows

A shadow is a dark shape, e.g. on the ground or a wall, caused by an object
or person, blocking light. Like a silhouette, the shape of the shadow is a
two-dimensional projection of the object.
For non-point sources of light, the shadow is divided into the umbra and
penumbra. The wider the light source, the more blurred the shadow. If there
are multiple light sources there are multiple shadows, with overlapping
parts darker. For a person or object touching the surface, like a person
standing on the ground, or a pole in the ground, these converge at the point
of touch.